HDPE closure welds/bolt-ups allowed per NFPA 24 hydro testing versus service testing?

[LNGDesigner]

All,

I had a question involving closure fusion welds or closure bolt-ups on a private fire main system. NFPA 24 states "all piping and attached appurtenances shall be hydrostatically tested" and basically thats all it says about testing. This is not very informative as i am used to B31.3 where all bases are covered as far as bolted connections used for blinding not subject to testing and a whole paragraph on allowing closure welds as long as the proper NDE is completed on the welds. I interpret this as all "piping and components are to be tested" but states nothing about testing "all joints" (i.e. required closure welds/bolt-ups in a tie-in) like B31.3 does.

It is almost impossible to test ALL joints on an underground fire main system, and more so when tie-ins are made to an existing underground fire system. NFPA 24 says nothing about this fact...so the question remains, are final closure bolt-ups and closure welds allowed and subject to service test only when no other viable options exist for adequate hydro testing?

What are others doing in this situation?

Thanks in advance for any help!

 

[stookeyfpe]

Your treating a fire service main as process piping. A fire service main designed in accordance with NFPA 24 has several significant difference when compared to ASME B31.3:

1) Specific limitations on allowable materials of construction
2) Piping, fittings and valves must be listed by a nationally recognized testing laboratory such as Underwriters Laboratories or Factory Mutual
3) Components must be rated for a minimum pressure of 150 PSIG
4) The standard only applies to water
5) The installation is subject to the approval of the authority having jurisdiction, which can vary by location. If your plant is in a area subject to fire code regulation, the Fire Marshal has the final authority. This is completely different in comparison to ASME B31.3 where the relationship is primarily between the owner and the engineer of record.

In fire protection engineers, isolation valves are commonly installed for lateral lines and at connections to the fire service main, such as fire hydrants or feed laterals to water based fire protection systems. A properly engineered lateral will have at least one isolation valve.

For PVC or HDPE piping, solvent welding and compression seals are generally the method of assembly. Assembly methods may also be dictated by the manufacturer of the pipe and fittings.

Trying to apply ASME B31.3 to fire protection water piping is adding a great deal of cost and complication that is not warranted in my mind.

 

[LNGDesigner]

I am not trying to apply one to the other, just using 31.3 as a reference. And one cannot hydrotest against an isolation gate valve in the first place, and at 225psi defintely not.

So how does NFPA 24 code treat closure fusion welds or bolt-ups when they cannot be hydrotested feasibly? Are they completely not allowed even though the code doesnt state it?

 

[stookeyfpe]

My 25+ years of experience has included hydrostatic testing of hundreds of fire service mains filled with water with one or more isolation valves being closed while subjecting the system to pressures of 200-250 PSIG. So our experience is completely opposite.

So how does NFPA 24 code treat closure fusion welds or bolt-ups when they cannot be hydrotested feasibly?

The standard doesn't address it. I can't remember an installation as to when this has occurred. In this case, alternate testing methods may be in order. NFPA 24, Section 10.10.2.3 permits the use of American Water Works Association (AWWA) standards, but these standards also prescribe hydrostatic pressure tests. In such a case, one could apply one of the test methods used in ASME B31 as an alternative method of compliance. In such a case, approval of the alternative method by the Authority Having Jurisdiction would be required if NFPA 24 was adopted by a governmental authority.

 

[LNGDesigner]

Ok, thanks stookeyfpe for the info. Ya i read that you could go to AWWA in some instances, but that wouldnt help me much. And yes i have seen the gate's leak by too fast for a proper test, typically ones that have been in service for a while. Even NFPA 24 states that code prefers you not test against a gate valve, and why 31.3 doesnt allow it at all. There are some instances where testing an old line to 225 to capture a few new fusion welds would open a whole other can of worms, but code does say test a repair like a new connection.

In my honest opinion allowing a few closure welds or bolt-ups is always a necessary evil. I wish NFPA 24 addressed this in some way. It is almost impossible to build a very large fire main system and pressure test the entire system after individually testing segments upon installation, and even then you must remove the testing blind with the tree and make that final bolt-up to close the system in which that final bolt-up is subject to a service test only, and that final bolt-up joint technically hasnt been pressure tested and therefore "not allowed" by code.

You seem to be an expert with this code, so is your interpretation of "all piping and attached appurtenances shall be hydrostatically tested" mean not only all piping and components, but ALL joints tested as well, no exceptions?

 

[cdafd]

LNG,,

Guess I have been around plastic pipe for along time. Can I ask what part of the country this is being installed in?

 

[LNGDesigner]

Southern region